The Geology of Chaco Canyon, New Mexico In Relation To The Life And Remains Of The Prehistoric Peoples Of Pueblo Bonito Smithsonian Miscelleanous Collections Volume 122, Number 7

All peoples known to have occupied Chaco Canyon in prehistoric times were dependent for sustenance largely upon agriculture. The Navaho now living there are principally stock raisers, but nearly all of them plant fields of a sort. Two small patches of corn were to be seen near Pueblo Bonito in 1924; farther upstream, beyond Pueblo Pintado, fields were larger and more numerous. The Bonitians, however, lacked domestic animals and although the hunting in their day may have been better than it is now the major part of their food supply doubtless came from cultivated plots.

As pointed out heretofore, the present climate of the Chaco area is unfavorable to agriculture by reason of the unreliability of rainfall, particularly in June and July, and because of the comparatively short growing season. Elsewhere irrigation makes possible the growth of most crops common to the temperate region; corn, beans, and squash, still staples of Indian tribes throughout the Southwest, are known from frequent finds in excavations to have been the main crops in prehistoric times. During the course of this investigation we were constantly on watch for evidence of local irrigation with living water—and found none.

The floor of Chaco Canyon has no irregularities that are not entirely natural in origin except wagon roads, mounds covering ruins, and an ill-advised ditch built some years ago by a white man. The banks of the modern arroyo were carefully inspected for traces of ancient irrigation ditches but none was found in the main valley fill. Such negative evidence would be of little value were it not a fact that in every country in which living water is used for irrigation the ditch banks are routes of travel and are thereby compacted. It is inconceivable that, if ditches had been used by the ancient inhabitants of Chaco Canyon, all their compact ditch banks would have been destroyed, especially when the processes of alluviation were so gentle that char coal in hearths was buried with little disturbance. Under such conditions the hard-packed surfaces of ditch banks should also have been preserved.

Materials of the valley fill, as already described, do not indicate that there ever was a stream of living or perennial water in Chaco Canyon during the two periods of alluviation determined by these investigations. Such materials all appear to have been laid down during muddy floods similar to those now characteristic of Chaco River. Irrigation by means of a system of ditches continuously maintained is hardly practical on such a stream. Thus geologic interpretation confirms the negative evidence of the ditches and indicates that the prehistoric peoples of Chaco Canyon did not practice irrigation as we commonly understand it. However, in selected places they could have farmed successfully by irrigating with flood water or, as it is usually called, "floodwater farming." For this method the floor of Chaco Canyon, save for the presence of its modern arroyo, is entirely suitable.